Subtitles displayed by rendering a graphics stream are important means for people in different linguistic areas to enjoy foreign-language films. Such a graphics stream is multiplexed with a video stream that represents a moving picture, and recorded on a recording medium. The graphics stream includes a plurality of display sets that are each made up of display control information and graphics data. Each of the display sets is used for displaying an individual subtitle in reproduction of a film. The display sets are read from the recording medium and processed one by one as the reproduction of the moving picture progresses, to display the subtitles together with the moving picture.
Here, if each display set is processed only after processing of an immediately preceding display set is completed, a processing delay develops. Thus, when the graphics stream contains multiple display sets, the need for parallel processing of display sets arises.
Subtitles have a property of changing as the moving picture progresses. This being so, when two display sets are processed in parallel, a subtitle to be displayed later may be decoded at the same time as a subtitle to be displayed earlier. As a result, the subtitle to be displayed later may end up being displayed in place of the subtitle to be displayed earlier. Thus, even if a reproduction apparatus is capable of processing display sets in parallel, such a capability is useless unless the original display order of subtitles is maintained.